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1. Field of Invention
This invention relates to a camera, specifically to a mirror apparatus for the viewfinder of a single-lens-reflex camera.
2. Description of Prior Art
Typical single-lens-reflex (SLR) cameras have an optical system comprised of an objective lens, a pivoted movable mirror to reflect an inverted image upward to a viewing screen, and optics (a pentaprism) to erect the inverted image and direct it to an eyepiece. The user can then compose and focus the image on the viewing screen. The typical SLR camera also includes hardware to pivot the mirror out of the path of the image so the image can pass through the camera to a focal plane shutter and fall upon a light-sensitive surface at the back of the camera, and thereafter to reposition the mirror back to its original position for subsequent camera operations. The advantages of this system, compared to a rangefinder type camera, are that parallax misalignment is eliminated, and focusing and composing are easier.
However, the SLR camera system has serious disadvantages:
a) The hardware to pivot or otherwise move the mirror is complex and space-consuming. The mirror must be pivoted so its moving arc clears the objective lens, which means the mirror must be smaller, or the camera larger than would ideally be the case
b) The rapid and abrupt manner in which the mirror must pivot up and then down causes shock and vibration as the mirror impacts its hardware. This vibration makes it difficult to get a high resolution image on the film.
c) The noise generated by the mirror impacting its hardware makes wildlife and certain other types of photography difficult.
Some solutions of these problems have been proposed by the following: Ochai and Kato (U.S. Pat. No. 3,757,661, granted Sep. 11, 1973), Ohmori (U.S. Pat. No. 3,911,454, granted Oct. 7, 1975), and Kanno (U.S. Pat. No. 5,715,003, granted Feb. 3, 1998), have devised a mechanism for sliding the mirror horizontally out of the picture frame. Waaske (U.S. Pat. No. 3,967,290, granted Jun. 29, 1976), Schiff and Rikis (U.S. Pat. No. 3,785,270, granted Jan. 15, 1974), Sadre-Marandi et al. (U.S. Pat. No. 4,659,202, granted Apr. 21, 1987), and Lindenfelser (U.S. Pat. No. 4,750,012, granted Jun. 7, 1988), have devised a mechanism for sliding the mirror vertically out of the picture frame. Celenze (U.S. Pat. No. 4,758,853, granted Jul. 19, 1988) has a combination flexible mirror/shutter, which reflects the image to a viewfinder, then displaces to present a slot through which the image reachs the film. Although these mechanisms solve some of the problems mentioned above, none solve the problems of vibration and noise, and they are generally complicated, bulky and space consuming.
Also, a camera using a fixed, half-silvered pellicular mirror has been sold by Canon under the trademark Pelix. This camera solves the vibration problem, but at the expense of a compromised image brightness on the viewfinder screen and on the film surface.
Accordingly, one object of this invention is to overcome the shortcomings and disadvantages of the typical single-lens-reflex camera by:
a) virtually elilnating vibration and noise in the mirror moving mechanism of an SLR camera, making higher resolution images possible,
b) providing an SLR camera with a simple mirror moving apparatus which is very rigid and rugged, with few moving parts, which will keep the mirrors in alignment under the most severe conditions, assuring increased reliability and trouble-free service, and
c) providing an SLR camera in which the mirror is close to the rear of the objective lens, allowing a larger mirror, and a brighter image on the viewing screen, as well as a smaller and more compact camera.
Other advantages will become apparent from reading the following sections and perusing the accompanying drawings.
A simple and rugged mirror system for an SLR camera virtually eliminates camera movement, noise, and vibration caused by mirror action. It utilizes a pair of dynamically balanced bi-parting sliding mirrors, which, in a contiguous (normal) position reflect an undistorted image to the viewing screen, and which slide apart to allow the image then to pass through an aperture to the rear of the camera to record the image. Thereafter they return to their contiguous position.